Abstract: For the purpose of determining the effects of slope gradient on its plant community diversity, some investigations were conducted with the Line Transect Method in 2010 along five roads surrounding Chengdu city. A total of 101 slope quadrats were investigated. These slopes have an altitude between 300-400 m and the same soil texture. The results showed that: (1)within the quadrats, there were 142 species of plants, belonging to 61 families and 121 genera. Sixteen genera and 19 species belonged to Compositae; Gramineae had 14 genera and 16 species; Leguminosae consisted of 9 genera and 11 species; Rosaceae had 4 genera and 7 species. These four families totally had 43 genera and 53 species, which account for 37% of the total species; (2)slope gradient had significant effect (P<0.05) on the species diversity of shrub and herb layer of both sunny and shady slopes; (3)community evenness index of shady slope was significantly influenced by slope gradient (P<0.05); to the richness of sunny slope community, its influence was significant. Analysis showed that the influence of gradient on the community diversity of roadside slopes surrounding the Chengdu Plain was significant; on the slopes where gradients were below 35°, vegetation community recovered well and the diversity of community was high; when the gradient was above 35°, diversity indexes declined rapidly, which made vegetation restoration harder.

Key words: gradient, slope, plant diversity, road